Paleodiet in northern Chile through the Holocene: extremely heavy δ15N values in dental calculus suggest a guano-derived signature?

Dental calculus extracted from the teeth of 28 prehistoric human skeletons from coastal and valley archaeological sites in northern Chile that date from the Archaic period (similar to 2300 BC) to the Late Intermediate period (AD 1476) was analyzed for stable isotope (delta N-15, delta C-13) compositions. delta N-15 compositions were extremely heavy (+17.8 to +33.1 parts per thousand), but comparable to some studies using conventional human biomaterials (hair, nail, muscle) at other prehistoric sites in northern Chile. There was a negative correlation between delta N-15 and delta C-13 for coastal sites, but a positive correlation for valley sites. Results for the valley sites point to a diet that was influenced by marine resources throughout all time periods. The unusually heavy delta N-15 values for the coastal sites require a dietary component with a delta N-15 composition significantly heavier than that of marine resources. The hyper-aridity at the study area (mean annual rainfall of 0.5-0.6 mm/year) is a likely contributing factor to the production of heavy delta N-15 values, but is unlikely to account for the heaviest delta N-15 values (>+30 parts per thousand). One possible explanation for the heaviest delta N-15 values is that dietary components were impacted by isotopically-heavy guano, which is abundant in the region. Guano may have been used as a fertilizer during crop cultivation at the onset of the Formative period, continuing through the Historic period after Spanish contact. The indirect impact of guano from abundant bird habitats in the region may have influenced wild foodstuffs harvested throughout the pre-agricultural period. Results provide support for the utility of dental calculus as a proxy for obtaining stable carbon and nitrogen isotope signatures for use in paleodietary studies. (C) 2013 Elsevier Ltd. All rights reserved.